1. Field of the Invention
The present invention relates to a liquid chromatography apparatus, or more in particular to a high pressure liquid chromatography apparatus comprising liquid-supply means adapted for supplying a liquid mobile phase to a column by means of a dual pump, i.e., two reciprocating piston pumps.
2. Description of the Prior Art
In a liquid chromatography apparatus comprising a dual pump for supplying a liquid mobile phase to the column, it is well known to produce the output flow of the pump, i.e., to accomplish the pumping operation without pulsation in order to carry out with high accuracy the quantitative analysis of the specimen components separated by the column.
An example of such an apparatus is disclosed in U.S. Pat. No. 3,917,531 entitled "Flow Rate Feedback Control Chromatograph". In the dual pump used in this patent, the production of the output flow of the pump, i.e., the pumping can be accomplished without pulsation, while the input flow of the pump, i.e., the filling thereof cannot be accomplished without pulsation. Therefore, in the case where two liquid mobile phases are programmably mixed by the method controlling opening time of two valves which are put on the suction side of the pump, the liquid mobile phase mixture ratio cannot be exactly proportioned to the opening time of the valves.
In FIG. 1 showing the flow pattern of the two pistons of the dual pump, pistons Nos. 1 and 2 of the above-mentioned U.S. Patent, the abscissa represents time and the ordinate the time derivative of displacement of the pistons dx/dt, where X shows the displacement of the pistons. Let the maximum value of dx/dt at the time of pumping of pistons Nos. 1 and 2 be j, and the value dx/dt during the overlap of the pumping operation of pistons Nos. 1 and 2 be l and k respectively. As seen from the graph, relation k+l=j is established during the pumping overlap. According to the dual pump disclosed in the cited U.S. Patent, therefore, the output flow of the dual pump, that is, the pumping operation is accomplished without pulsation. During the input flow, i.e., the filling operation of the dual pump, however, both pistons Nos. 1 and 2 fail to fill at the portion designated as n in the drawing. The presence of this portion n disables the filling operation without pulsation in the cited U.S. Patent.
As a result, the liquid chromatography apparatus disclosed in U.S. Patent has a disadvantage in the suction of liquid mobile phase as mentioned above.